The present invention relates to an electric axial flow machines as defined in the precharacterizing clause of the independent patent claim 1.
1. Field of the Invention
An electric axial flow machine is understood as meaning a motor or generator with a rotor and a stator, in which the magnetic flux between the rotor and the stator is parallel to the axis of rotation of the rotor. Axial flow machines of this type are also known by the designations brushless DC motor, permanent-magnet synchronous motor or disk-armature motor.
An efficient brushless DC motor with an ironless rotor arranged around a shaft and having permanent magnets is described for example in DE-U-298 16 561. In the case of this DC motor, arranged around the shaft on both sides of the disk-shaped rotor, and parallel to the rotor, there is in each case an electromagnet unit as a stator. The rotor has permanent magnets which are arranged in a circular manner around the shaft, are embedded for example in a plastic and the direction of magnetization of which runs parallel to the shaft. Two neighboring permanent magnets respectively have a reversed direction of magnetization. One stator is provided with first electromagnetic regions and the other stator is provided with second electromagnetic regions, the number of which corresponds to the number of permanent magnets, two neighboring first electromagnetic regions and two neighboring second electromagnetic regions in each case having reversed directions of magnetization, which are changed alternately. The first and second electromagnetic regions are arranged offset in relation to one another and have a phase difference of 90xc2x0.
One disadvantage of this DC motor is that the rotor is, by its nature, relatively unstable and therefore suitable only for slow rotations.
U.S. Pat. No. 5,619,087 discloses an electric axial flow machine which comprises at least two ironless disk-shaped rotors with relatively small, bar-shaped permanent magnets, which are embedded in a fiber- or fabric-reinforced plastic. A plurality of like-magnetized permanent magnets arranged next to one another respectively form a group, which forms one magnetic pole. The fact that many relatively small permanent magnets are arranged in the plastic instead of a number of large magnets has the effect of reducing the effective magnetic area, and consequently the magnetic flux, which is compensated by the use of at least two rotors. Furthermore, the anchoring of the many individual permanent magnets in the plastic presents problems in terms of production and strength.
In view of the disadvantages of the previously known axial flow motors and generators, the invention is based on the following object. The aim is to provide an electric axial flow machine, the rotor of which is as low in mass and inertia as possible, but nevertheless stable and also suitable for high rotational speeds.
An important feature of the invention is that, in an electric axial flow machine with an ironless disk-shaped rotor which is arranged on a machine shaft and has permanent magnets which are embedded in a fiber- or fabric-reinforced plastic, the permanent magnets are each joined with a positive fit to the surrounding fiber- or fabric-reinforced plastic and the latter, together with the permanent magnets and the machine shaft, forms a dimensionally stable unit. Arranged next to the rotor on both sides there is in each case a stator.
The mere fact that the plastic is fiber- or fabric-reinforced means that the rotor has great rigidity. This is further increased by the fact that the permanent magnets are each joined with a positive fit to the surrounding fiber- or fabric-reinforced plastic and the latter, together with the permanent magnets and the machine shaft, forms a dimensionally stable unit. The latter can be achieved by suitable arrangement of the permanent magnets and the machine shaft and molding of the fiber- or fabric-reinforced plastic. The design of the rotor according to the invention makes the rigid permanent magnets serve at the same time as stiffening elements, it being ensured by the positive connection with the surrounding plastic that the permanent magnets do not become detached.
A plurality of permanent magnets are advantageously arranged in a circular manner around the machine shaft, and the plastic, in particular a thermosetting material, advantageously extends between the permanent magnets altogether over at least 10%, preferably between 15% and 20%, of the circle. By arranging and embedding the permanent magnets in such a way, the rotor can be optimally designed with regard to strength and efficiency.